Regression tests using outdated version of Veryl.

[nblei]

  × Unexpected token: ':'
   ╭─[/home/runner/work/std/std/src/async_fifo/async_fifo.veryl:7:26]
 6 │ /// Generic parameter `S` is a module name of synchrinozer.
 7 │ pub module async_fifo::<S: synchronizer> #(
   ·                          ┬
   ·                          ╰── Error location
 8 │     param WIDTH             : u32  = 8                         , /// Data width
   ╰────

[dalance]

Yes. This is one of motivations of #17.
I'll change Veryl of CI from stable release to github temporaly.
After merging #6 and #19, I'll do #17.

[dalance]

Regression failure was fixed.